Aminex, the Africa and US focused oil and gas firm, is seeking to complete a so called 'acreage swap' in Tanzania with its partner, Key Petroleum.In essence, the deal will see Aminex's 50% stake in the Songo-Songo transferred to its partner Key Petroleum after what the company describes as "slow progress" in developing the field.In return Aminex will receive Key's 5% stake in the Nyuni area. Both sites are off Tanzania's east coast and the two companies are waiting for official approval by the Tanzanian authorities.Aminex's shares were down nearly 2% in early trading.BS